This invention relates to thin film inductive transducers, and more particularly to those suitable for perpendicular recording and reading of magnetic transitions on a moving magnetic recording medium.
Various configurations have heretofore been proposed to enhance efficiency of thin film inductive transducers during recording and to enhance the resolution of transitions during reading. Thin film inductive transducers suitable for conventional longitudinal recording consist of two magnetic layers providing a single gap head. A typical transducer of this type is disclosed in U.S. Pat. No. 4,190,872.
There has been increasing interest, however, in transducers suitable for perpendicular recording and reading because perpendicular recording has the potential of providing higher linear recording densities than are possible with conventional longitudinal recording.
In the IEEE Transactions on Magnetics, dated September 1980, at pp. 967 et seq., there is published a paper entitled "Self-Consistent Computer Calculations for Perpendicular Magnetic Recording" by R. I. Potter and I. A. Beardsley. In this paper analytical expressions are discussed for calculating magnetic fields for four types of recording heads considered for perpendicular recording: (a) ferrite head; (b) thin film head (of the single gap type); (c) double gap head (of the ferrite type); and (d) a single pole head and soft magnetic substrate. In this paper, a single gap thin film head is shown in FIG. 15; and FIG. 16 depicts a double gap head having a thin center pole tip but outer pole tips apparently of infinite width, which (like in FIG. 3 entitled "Ferrite Head") would be appropriate only for a double gap ferrite head. The location of the conductive turns and the overall configuration and method of fabrication of the head are not disclosed or suggested.
Thin film inductive transducers previously proposed for perpendicular recording and known to applicant are of the single gap type employing two magnetic layers. They undesirably produce a "dibit" pattern of magnetic transitions which is difficult to detect. Also, a phenomenon known as "wrap-around" described in U.S. Pat. No. 4,219,855 may occur with thin film heads. This phenomenon occurs due to misregistration of the magnetic layers at the pole tip during deposition. As a result, the edge portion of one layer overhangs at an angle the edge of the other layer, causing an undesirable reduction in the effective width of the said one layer and hence in efficiency of recording and reading.
No prior art known to applicant suggests a double gap thin film inductive transducer which is relatively easy to manufacture and which is especially suitable for high linear density perpendicular recording and reading. A thin film double gap head is preferable over a double gap ferrite head because the thin film head provides higher performance. It employs Permalloy magnetic material which provides higher frequency response than ferrite material; and since it is smaller, a thin film head has less inductance.